A darling of the international community, the 72-year-old is less popular at home however and the award she shared with two other women -- fellow Liberian Leymah Gbowee and Yemen's Tawakkul Karman -- could come as a much-needed boost in Sunday's elections.
Since landing at the helm of a nation traumatised by 14 years of brutal civil war with no electricity, running water or infrastructure, Sirleaf has earned international praise.
The sprightly grandmother, typically dressed in flowing robes and headdresses has reinforced her "Iron Lady" moniker as she charmed financial institutions to write off billions of dollars in debt and ushered in investors.
Sirleaf declared corruption a public enemy and set about her goal of institutional reform with the steely determination which saw her thrown into jail twice by military dictator Samuel Doe in the 1980s.
However turning around Africa's oldest independent state, which had become rotten to the core, was never going to be easy.
While warmly welcomed abroad and feted much like a female Nelson Mandela, a string of corruption scandals, lack of national reconciliation efforts and perceived broken promises have seen attitudes cool towards Sirleaf at home.
She has so far ignored a 2009 report by the country's Truth and Reconciliation Commission which named her on a list of people who should not hold public office for 30 years for backing warlord-turned-president Charles Taylor.
Sirleaf has admitted to initially backing Taylor's insurgency against Doe's government in 1989 which led to the country's first civil war, but became a fierce opponent as the true extent of his war crimes became apparent.
Shortly after the TRC report was released, Sirleaf announced she would be seeking a second term in office to continue rebuilding the nation -- after initially pledging to serve only one -- prompting a storm of criticism from the opposition.
"We still have a long way to go, but we have succeeded in restoring a good amount of basic infrastructure," she recently told the Jeune Afrique magazine.
Half of the roads around Monrovia have been rebuilt and the capital now has running water. Once non-existent, some parts of the capital have access to electricity but the supply is haphazard.
But unemployment is still at about 80 percent and extreme poverty pervasive.
"President Sirleaf is not popular here as she is internationally because she really did not try to address the major concerns of the population," civil servant Abel Nyumah, 45, told AFP in Monrovia.
"The price of rice today is five times higher than Taylor's time."
A Harvard-trained economist, Sirleaf served as finance minister under presidents William Tolbert then William Tubman, before spending decades shuttling in and out of exile. She has also worked for the World Bank.
Sirleaf -- who has devoted herself to fighting gender violence -- was married at age 17, and later divorced after the relationship turned abusive. She has four sons and eight grandchildren.
Lansana Gberie, a West Africa Research Analyst with the Security Council Report in New York, got to know Sirleaf while she was in exile in Abidjan.
"I always thought that she had a strong feel for the sentiments/anxieties of the grassroots -- she can alternate between the upper class Liberian accent and the uneducated streetwise or rural ones," he told AFP.
"Then came power, and the demands of running a completely bottom-out state."
He said Sirleaf has been let down by those she recruited from the diaspora -- seeking competent, educated hands -- who proved "disastrous, corrupt and inefficient."
Gberie said Sirleaf had concentrated on rebuilding the visible structures of the state, to the detriment of reconciliation
"That is the problem she is now facing, and it does appear that she is rather unpopular in the country. Her re-election, which I wish for, is certainly not assured."